Variations in temperature can affect component parts of a microwave system causing differences in signal strength at different temperatures and frequencies. Much time, effort and expense has gone into the design of components of such systems in an effort to stabilize them over various temperature and frequency ranges. This has greatly increased the cost of microwave systems that must be exposed to wide temperature ranges.
Rather than attempt to stabilize the signal level of a microwave circuit by optimizing each component part thereof, an alternative strategy is to allow the signal level to vary over temperature and frequency but to stabilize the signal using an attenuator having temperature and frequency dependent attenuation that offsets the temperature and frequency variations in the microwave circuit. Thus, the attenuator solves the stability problem by flattening the linear increase in attenuation or (decrease in gain) with frequency and temperature.
One example of an absorptive-type temperature variable attenuator is the attenuator described in U.S. Pat. No. 5,332,981 entitled, “Temperature Variable Attenuator,” which is incorporated herein by reference. Examples of the attenuator of the '981 patent include a Tee attenuator and a Pi attenuator. In each case at least one resistor has a temperature coefficient of resistance (TCR) that is different from that of the others such that the attenuation of the attenuator changes at a controlled rate with changes in temperature while the impedance of the attenuator remains within acceptable levels.